[doc/tracepoint] Add a note for assigning values of inferior to trace state variables

[Hui Zhu <teawater@gmail.com>]

Hi,

I talk about a bug about assigning values of inferior to trace state variables
http://sources.redhat.com/ml/gdb/2011-07/msg00009.html

this issue can be handle by convert value to (uint64_t), for example:
teval $tmp=(uint64_t)a

So I make a patch to update the doc.

Please help me review it.

Thanks,
Hui

2011-09-16  Hui Zhu  <teawater@gmail.com>

	* gdb.texinfo (Tracepoint Action Lists): Add a note for assigning
	values of inferior to trace state variables.

---
 doc/gdb.texinfo |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/doc/gdb.texinfo
+++ b/doc/gdb.texinfo
@@ -10321,6 +10321,12 @@ are discarded, so this is mainly useful
 state variables (@pxref{Trace State Variables}) without adding those
 values to the trace buffer, as would be the case if the @code{collect}
 action were used.
+Please note that if you want assigning values of inferior to trace state
+variables, please convert it to unsigned 64bit first.  For example:
+
+@smallexample
+>teval $c=(uint64_t)jiffies_64
+@end smallexample

 @kindex while-stepping @r{(tracepoints)}
 @item while-stepping @var{n}